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The invention relates to the preparation of formylphosphonic acid and its related compounds. The invention also relates to a method of making glyphosate, its related compounds, and products thereof.
N-phosphonomethylglycine, also known as glyphosate, is a highly effective and coimmercially important herbicide useful in controlling the growth of germinating seeds, emerging seedlings, maturing and established woody and herbaceous vegetation, and aquatic plants. Glyphosate is typically applied in the form of an aqueous solution of a salt thereof as a post-emergent herbicide for the control of growth of monocotyledonous and dicotyledonous plant species. Herbicidal salts of glyphosate and use thereof are described, for example, in U.S. Pat. No. 4,405,531.
Various methods for the production of glyphosate are known. For example, it can be produced by oxidizing N-phosphonomethyliminodiacetic acid in the presence of a catalyst. A variety of catalysts are known to catalyze such oxidation reactions. Glyphosate can also be produced by first reacting formylphosphonic acid (FPA) with glycine to form a condensation product and then hydrogenating the condensation product, for example, as described in U.S. Pat. No. 4,568,432. The latter synthetic route for glyphosate is desirable because a relatively high yield can be obtained. However, one limitation of this process is that the starting material, formylphosphonic acid, is not commercially available, and the methods known in the art for producing it suffers from one or more limitations.
For example, formylphosphonic acid is produced as a by-product in the electrochemical oxidation of nitrilotris-(methylenephosphonic acid) or substituted iminodimethylenediphosphonic acids to a secondary amine. This reaction requires the addition of a strong hydrochloric acid solution which presents safety, environmental, and equipment corrosion problems. Electrochemical methods generally require an external power source and other equipment which typically have higher maintenance needs and costs than non-electrochemical reactions.
Another known process in which formylphosphonic acid is produced as a by-product involves oxidation of tertiary phosphonomethylamines by oxygen in the presence of an activated carbon catalyst to cleave a phosphonomethyl group and to produce a secondary amine. Formylphosphonic acid may be produced as an intermediate cleavage fragment, with the fragment undergoing hydrolysis in a second step to form formic acid and phosphorous acid. Since a secondary amine is produced in the process, its presence necessitates additional steps, such as separation or recycling, which may result in manufacturing complexities.
Therefore, there exists a need for a new method for producing formylphosphonic acid and related compounds in an effective manner.
The aforementioned need is met by embodiments of the invention in one or more of the following aspects. In one aspect, the invention relates to a process of making a phosphorus-containing compound. The process comprises contacting a hydroxymethylphosphonic acid compound with an oxidant in the presence of a catalyst to produce a formylphosphonic acid compound or its hydrate. The hydroxymethylphosphonic acid compound is represented by Formula I below: 
wherein Rxe2x80x2 and Rxe2x80x3 individually are hydrogen, hydrocarbyl, substituted hydrocarbyl, a salt-forming cation, or a heterocycle; the formylphosphonic acid compound is represented by Formula II below. 
In some embodiments, the oxidant is replenished during the contacting. The process may further comprise reacting the formylphosphonic acid compound with a nitrogen-containing compound represented by Formula III below 
to produce a condensation product, wherein n is 0 or any positive integer, and R is xe2x80x94H, xe2x80x94OH, xe2x80x94CONH2, xe2x80x94NH2, xe2x80x94COOH, hydrocarbyl, substituted hydrocarbyl, a salt-forming cation, or a heterocycle, provided that when R is xe2x80x94COOH n is not zero. When n equals to 0 and R is xe2x80x94CONH2, the nitrogen-containing compound is urea, and the condensation product is hydrogenated and converted to a glyphosate compound. When n equals to 1 and R is xe2x80x94COOR1, the nitrogen containing compound is a primary amine represented by Formula IV: 
wherein R1, is hydrogen, hydrocarbyl, substituted hydrocarbyl, a salt-forming cation, or a heterocycle. In this embodiment, the process may further comprise hydrogenating the condensation product to produce a glyphosate compound represented by Formula V below. 
When n equals to 0 and R is hydrogen, the nitrogen-containing compound is ammonia, and the condensation product is hydrogenated to form an aminomethylphosphonic acid compound represented by Formula VI below. 
In this embodiment, the process may further comprise converting the aminomethylphosphonic acid compound to a glyphosate compound represented by Formula VII below. 
When n is 2 and R is xe2x80x94OH, the nitrogen-containing compound is ethanolamine, and the condensation product is hydrogenated to form a hydroxyethylaminomethylphosphonic acid compound represented by Formula VIII below. 
In this embodiment, the hydroxyethylaminomethylphosphonic acid compound is oxidized to form a glyphosate compound represented by Formula VII. The glyphosate compound or one or more salts thereof so obtained may be admixed with one or more additives to produce a herbicidal formulation.
In some embodiments, the oxidant is O2 or H2O2. Substantially pure oxygen, oxygen mixed with a carrier gas, or air may be used as an oxidant. In other embodiments, the hydroxymethylphosphonic acid compound is hydroxymethylphosphonic acid, and the formylphosphonic acid compound is formylphosphonic acid. The catalyst may be homogeneous, heterogeneous, supported, or unsupported. The catalyst may be an iron-containing compound, such as ferrous sulfate; a copper-containing compound, such as metallic copper, sponge copper, or Mo-doped copper; or a titanium-containing compound. The process may be conducted in the presence of a solvent, such as an aqueous solution or a non-aqueous solution. It may also be conducted in the presence of an acid or a base. The pH of the resulting mixture may be less than about 7, less than about 5, less than about 2, or less than about 1. The process may be conducted at a temperature of less than about 200xc2x0 C., less than about 150xc2x0 C., less than about 100xc2x0 C., or less than about 50xc2x0 C. In some embodiments, the oxidation reaction occurs electrochemically between the hydroxymethylphosphonic acid compound and the oxidant.
In another aspect, the invention relates to a process of making formylphosphonic acid. The process comprises contacting a hydroxymethylphosphonic acid with an oxidant in the presence of a catalyst to produce a formylphosphonic acid. The hydroxymethylphosphonic acid may be obtained by reacting formaldehyde with phosphorous acid. The oxidant may be O2 or H2O2. The catalyst may be copper. In some embodiments, the oxidation reaction occurs electrochemically between the hydroxymethylphosphonic acid and the oxidant.
In still another aspect, the invention relates to a process of making glyphosate, a salt thereof, or a glyphosate precursor compound. The process comprises contacting a hydroxymethylphosphonic acid with oxygen or hydrogen peroxide in the presence of a catalyst to produce a formylphosphonic acid; and contacting the formylphosphonic acid with a reactant selected from the group consisting of ammonia, glycine, ethanolamine, and salts thereof to form a condensation product. When glycine or a salt thereof is used as the reactant, the condensation product is hydrogenated to form glyphosate or a salt thereof. When ammonia or a salt thereof is used as the reactant, the condensation product is hydrogenated to form aminomethylphosphonic acid or a salt thereof. The aminomethylphosphonic acid or a salt thereof may be carboxymethylated to form glyphosate or a salt thereof. When ethanolamine or a salt thereof is used as the reactant, the condensation product is hydrogenated to form hydroxyethylaminomethylphosphonic acid or a salt thereof. The hydroxyethylaminomethylphosphonic acid or salt thereof is oxidized to form glyphosate or a salt thereof The obtained glyphosate or one or more salts thereof may be admixed with one or more additives to produce a herbicidal formulation.
The hydroxymethylphosphonic acid may be obtained by reacting formaldehyde with phosphorous acid. The oxidant may be O2 or H2O2. It may be substantially pure oxygen, oxygen mixed with a carrier gas, or air. The catalyst may be homogeneous, heterogeneous, supported, or unsupported. The catalyst may be an iron-containing compound, such as ferrous sulfate, a copper-containing compound, such as metallic copper, sponge copper, or Mo-doped copper, or a titanium-containing compound. The process may be conducted in an aqueous solution or a non-aqueous solution. It may be conducted in the presence of an acid or a base. The resulting mixture may have a pH of less than about 7, less than about 5, less than about 2, or less than about 1. The process may be conducted at a temperature of less than about 200xc2x0 C., less than about 150xc2x0 C., less than about 100xc2x0 C., or less than about 50xc2x0 C. In some embodiments, the oxidation reaction occurs electrochemically between the hydroxymethylphosphonic acid compound and the oxygen or hydrogen peroxide.